Our main objective is to study the sequence of events and factors which affect the formation of nerve-muscle and intraneuronal synapses in sparse cell cultures of embryonic muscle, spinal cord and sensory ganglia, placed in various combinations. Simultaneous microelectrode (recording, stimulating and iontophoretic) and time-lapse cinematographic techniques will be correlated with autoradiographic and electron-microscopic findings. Attempts to separate specific cell types by microdissection, velocity sedimentation and affinity columns in order to obtain "pure" cultures containing only one presynaptic and one postsynaptic cell type will be made. Long-term changes in synaptic efficacy and trophic interactions between synaptically connected cells and the limits of specificity in synapse formation will be explored. In addition, we will study the development of postsynaptic chemosensitivity, the regulation of chemoreceptor distribution and the role of postsynaptic receptors in synapse formation.